Vibratory drive mechanism



April 27, 1965. J. M. MORRIS 3,180,158

VIBRA'IORY DRIVE MECHANISM Filed Nov. 2. 1961 Fig,5

INVENTOR. JOHN M. MORRIS AITORNEYS United States Patent 3,180,158VIBRATORY DRIVE MECHANISM John M. Morris, Louisville, Ky., assignor toRex Chainbelt Inc, a corporation of Wisconsin Filed Nov. 2, 1961, Ser.No. 149,572 6 Claims. (Cl. 74-26) This invention relates to a vibratorydrive mechanism and in particular to means for adjustably controllingthe stroke of vibratory apparatus driven by a constant stroke crank andconnecting rod mechanism.

Many types of vibratory apparatus such as conveyors, feeders, vibratoryscreens, earth tampers, and similar apparatus are driven by crank andconnecting rod mecha nisms that provide a substantially constant strokeregardless of the variations in load or forces being overcome by thevibratory members. These drives are quite satisfactory as' long as it isnot necessary to vary the amplitude of the vibratory movement of thevibrating members. However these drives cannot be readily adapted forvariable amplitude operation.

The principal object of this invention is to provide means for varyingthe amplitude of vibration of a vibratory member driven by a constantstroke crank and connecting rod mechanism.

Another object of the invention is to provide means that are readilyadaptable for remote control for controlling the amplitude of vibrationof a vibratory member.

A still further object of the invention is to provide tunable couplingmeans between a crank and connecting rod mechanism and a tuned vibratorymember arranged so that at one condition of tuning there is no forcetransmitted from the crank and connecting rod mechanism to the vibratorymember.

A still further object of the invention is to provide means foradjustably controlling the amplitude of vibration of a vibratory memberregardless of the vibratory force requirements of the vibatory member.

A still further object of the invention is to provide tunable drivingmeans for driving a tuned vibratory system from a constant stroke drivemechanism arranged so that the tuning for zero force transmission fromthe drive mechanism to the tuned vibratory member occurs with asubstantial spring rate in the tunable drive means.

More specific objects and advantages are apparent from the followingdescription of a preferred form of the invention.

According to the invention, the drive force from a crank and connectingrod mechanism is divided into two parts by differential mechanism withone part being applied directly to the work member and the other partbeing applied to a mass that is coupled to the work member through anadjustable rate spring. The range of adjustment of the rate of thecoupling spring coupling the mass to the work member is such that at oneextreme the mass and spring form a resonant system having an extremelylow resonant frequency that is much lower than the operating speed andat another condition of tuning or adjustment of the rate of the springthey form a resonant system having a resonant frequency higher than theoperating speed. Ordinarily, the full range of tubing is not employedbut rather either one of the two ranges of tuning is used, one employingspring rates equal or greater than that providing zero forcetransmission and the other providing spring rates equal or less thanproviding zero force. The upper range of tuning is preferable forcontrol purposes because of the improved regulation of the system withrespect to changes in load when operating at full stroke.

A preferred form of the invention is illustrated in the accompanyingdrawings.

In the drawings:

FIG. 1 is a schematic side elevation of a vibratory conveyor or feederembodying a drive constructed according to the invention. 7

FIG. 2 is a schematic side elevation of a vibratory conveyor or feederemploying a preferred form of the invention employing pneumatic springsas the adjustable resilient elements.

FIG. 3 is a schematic diagram illustrating the general cooperation ofthe elements including the division of drive force between the twopaths.

FIG. 4 is a graph illustrating, in general, the variation in transmittedforce with changes in tuning of the coupling spring.

These specific figures and the accompanying description are intendedmerely to illustrate the invention and not to impose limitations on theclaims.

A vibratory system that includes the improved drive mechanism maycomprise a conveyor trough or feeder trough 1 that is supported frombase 2 by means of in clined struts or cantilever leaf springs 3 andcoil springs 4. The springs cooperate with the trough 1 to form avibratory system that is preferably tuned to be resonant near theoperating speed. Vibratory energy to drive the trough 1 is provided by arotating crank or eccentric shaft 5 that is journaled in a standard 6erected from the base 2. The crankshaft 5 is connected through aconnecting rod 7 to a lever 8 that is pivotally connected to a bracket 9depending from the conveyor 1. The lever 8 carries a mass It on itslower end, the mass being connected through an adjustable spring 11 tothe conveyor 1. The lever 8 is a form of. differential mechanism todistribute the force from the connecting rod.

The crankshaft 5, which may also be considered as an eccentric shaftbecause of its relatively short throw, is preferably driven at aconstant speed by means not shown. This constant speed should, for bestresults under load, be approximately 5 percent less than the natural orresonant frequency of the conveyor trough 1 on the springs 3 and 4.While coil springs 4 are shown as assisting the cantilever springs 3 inproviding the resilient force for the conveyor trough 1, other types ofsprings may be substituted or the cantilever springs 3 may be made stiffenough to provide all of the force themselves. The system is tuned inthis manner so that the connecting rod 7 and crankshaft 5 need notsupply the inertia forces required to vibrate the deck or trough 1.

Forces from the connecting rods 7, applied to the lever 8, are dividedwith one component being applied to the bracket 9 at the upper end ofthe lever and thus applied directly to the conveyor trough 1 whereas theothercomponent of the force is applied to the mass 10. Any movement ofthe mass 10 transmits a force through the adjustable spring 11 to theconveyor trough 1. By adjustment of the adjustable spring 11 themagnitudes of the forces applied to the conveyor trough 1 may be variedover a wide range and thereby vary or control the amplitude of vibrationof the trough 1 while the stroke of the eccentric or crankshaft 5 andconnecting rod 7 remains constant. 'When the. adjustable spring 11 isadjusted for a very low spring rate the mass 10 tends to form a-fulcrumfor the lever 8 and the force transto the conveyor deck 1 in accordancewith the spring rate and the deflectionof the mass 10 from its neutralposition. This spring force acts in opposition to the linearly as theheight'of the spring decreases.

force transmitted through the lever and mounting bracket 9 to theconveyor :to thus reduce the net force applied to the conveyor-trough 1.

If the spring rate of the adjustable spring 11 is increased until thespring becomes very stifi, the mass moves in phase with the conveyordeck 1 and boththe lever fulcrum'9 and the spring 10 apply force inphase. to the conveyor deck 1. At anintermediate adjustment of thespring rate of the adjustable spring 11, the force transmitted throughtheadjustable spring 11 exactly counterbalances or is equal and oppositeto the force transmitted through the lever bracket 9 so that no force istransmitted from the connecting rod 7 to the conveyor trough 1. In thiscondition of tuning the lever mass 10 oscillates through an amplitude ofmotion which is greater than the motion of the connecting rod-inaccordance with the ratio of length of the arms of the lever 8 and theforce transmitted through:the connecting rod equals the inertia force ofthe mass 10. In order that the amplitude of motion of the conveyortrough 1 may be reduced practically to Zero when theforce transmissionthrough the lever and adjustable spring system is zero or approximatelyZero the :system comprising the conveyor trough 1 and the springs 3 and4 must not be. operated exactly at resonance.

Preferably the system -is tuned to a frequency slightly higher than theoperating speed.

FIG. 2 shows a similar arrangement in which pneumatic springs, arrangedto be variably inflated, serve as the adjustable rate spring 11. In thisparticular arrangement a conveyor trough .la is supported from a base 2aby means of cantilever leaf springs or struts 3a assisted by coilsprings 4a to form a tuned vibratory system having a natural frequencysubstantially at the operating speed.

This system is driven by a crank or eccentric shaft 5a mounted in adrive housing 6a and connected through a connecting rod 7a to a lever8a.The lever 8a is connected to the work member or trough 1a through alever fulcrum bracket 9a. 'The other end of the lever 81: carries a mass100 that is sandwiched betweena pair of air springs 12held in a bracket13 connected-to the work member or trough 1a. The lower endof thebracket 13 is braced by a' strut 14 to provide rigidity. The air'springs 12 are pneumatically connected through flexible connectionlines 15 and an adjustable pressure regulator 16 to an air pressuresupply pipe 17. It-is a charactersuch as those sometimes used asautomobile suspension springs, that the spring rate of an individualspring is not linear with displacement but rather increases non-However, when two air springs are used as a pair in opposition, asillustrated in the figure the nonlinear characteristics of onesubstantially cancels the nonlinear characteristics of the other so thatthe combination'presents a spring rate that is substantially constantwith displacement and which varies with the infiationpressure.

A single air spring can be used in this system provided that the otherair spring is replaced with a spring having a spring rate generallyequal to the spring rate of the air spring when inflated toapproximately half its maximum working pressure. Such a substitutedsystem performs in approximately the same manner except that the.neutral or rest position of the mass. 10a varies withthe inflationpressure. in this arrangement are quite smalland the use of a pair ofopposed air springs ispreferred. 1

FIGS. 3 and 4 are included to more clearly illustrate the dynamicconditionsthat exist in the drive constructed 'according'to theinvention. As illustrated in FIG. 3 a crank 20 having a radius R drivesa connecting rod 21 that is connected to an. intermediate pivot point ofa lever 22, the overall length of which is equal to B+C However, therange of spring rates available member is connected to ground throughthe spring 24' having a spring rate K The spring 24 is not equivalent tothe springs 3 and 4 but rather is an equivalent spring that representsthe tuned system comprising the work member 1 together-with the springs3 and 4 when operated at the operating speed of the crankshaft 5 andtuned to a frequency higher than the operating speed. The'spring'fidprovides force which is equal to the. dificrence between the springforce of the actual springs and the inertia force of the conveyor deckat the operating frequency.

. The second arm of the lever 22 having the length C is connected to amass 25 which in turn'is connected through an adjustable spring 26 tothemember 23. In the event the conveyor is tuned to have a resonantfrequency below the operating speed the spring 24 of FIG.

'21. Thus as the connecting rod 21approaches the right hand end of itsstroke with the mass 25 deflected to. the right from the position shown,it is being decelerated and the resulting force applied through thelever to the. member 23 acts toward the left. As the spring rate of thecoupling spring is increased from the zero condition, the spring appliesa force to the member 23 corresponding to the relative deflection of themass 25. Therefore, when the mass 25 is at the right hand end of itsstroke corresponding to the connecting rod 21 also being at the righthand end of its stroke, the spring 26 applies a force acting toward theright to themember 23 and thus in opposition to the force appliedthrough the lever and acting to the left. This condition is indicated inFIG. 4 which represents the net force applied to the work member or tothe spring 24 oil- 16.3 for various conditionsof tuning of theadjustable spring 26 corresponding to the adjustable spring 11 or theair springs 12. It may be noted that in this condition of tuning thework member 1 or the member 23 of FIG. 3 moves counter to the motion oftheconnecting rod 21 but at a lesser stroke; Thus the actual deflectionof the adjustable spring 26 is equal to the sum of the motions of themember 23 and the mass 25. This condition is illustrated by the branch30 of the .curve I shown in FIG. 4.

, mass 25 and the member 23 and therefore there isno rotation of thelever22 and both ends of the lever therefore apply force to the member23 in phase, the amount of the force developed depending upon the springrateand deflection of the spring 24 representing the tuned system.

This condition is indicated by the right hand end 31 of the curve shownin FIG. 4.

At an intermediate adjustment of the spring rate of the adjustablespring, a point 32 is reached at which there is no net force appliedfrom the connecting rod to' the Work member. if the spring 26 wereconnected between the mass 25 and a fixed point, the condition of tuningto accomplish the zero force transmission would occur when the spring 26and the mass 25 were in resonance with the speed of operation of thecrank29. If in the illustrated system the mass 25 and spring-26 areresonant at the operating speed and are driven to a substantialamplitude of vibration the force in the connecting rod 21 is quite smallbut the spring force of the spring 26 is applied to the member 23. Thisis a force in phase with the motion of the mass 25 and hence in phasewith the motion of the connecting rod 2-1 and would be a forcerepresented by a point on the branch of the curve between the point 32and the point 31. The point 32is reached, from the resonant condition,when the spring rate of the adjustable spring 26 is reduced in theproportion of the length C of the lever arm to the total length of thelever from the spring rate at which the mass 25 is resonant on thespring. This is the condition that the force transmitted through thelever directly to the member 23 is equal and opposite to the forcetransmitted through the lever and mass 25 and adjustable spring 26 tothe member 23.

In a practical use of this arrangement the mass 25 or the mass 19::sandwiched between the pneumatic springs is made quite small so that thequasi-resonant condition, the condition of no force transmission, occursat a relative low spring rate of the adjustable spring K. The operationis then confined to that branch of the curve in FIG. 4 lying between thepoints 32 and 31, the full amplitude of vibratory motion occurring nearthe point 31 which represents a practically direct connection betweenthe connecting rod 7 and the work member 1.

The advantages of this type of system over the use of the air springsdirectly in series with the connecting rod resides in the ability ofthis arrangement to reduce the transmitted force to zero with a non-zerospring rate as well as the provision of a substantially directconnection to the work member at the higher spring rates.

Various modifications of the arrangement shown may be made such asvarying the order of the pivots in the lever 8 without departing fromthe spirit and scope of the invention.

Having described the invention, I claim:

1. A vibratory drive system that comprises, in combination, a base awork member, resilient means supporting the work member from the base, adifferential mechanism having a first point connected to the workmember, a mass connected to another point of the mechanism, tunableresilient means connecting said mass to the work member, a crank shaftthat is journaled on the base, said crankshaft being operated at asubstantially constant speed and being connected to the differentialmechanism, and means for tuning said tunable resilient means.

2. A vibratory drive system that comprises, in combination, a base, awork member, resilient means supporting the Work member from the baseand cooperating with the work member to form a resonant system, a leverhaving a first point connected to the work member, a mass carried on thelever remote from the first point, tunable resilient means connectingthe mass to the work member, a crankshaft journaled on the base that isrotated at a speed that is near but not equal to the resonant frequencyof the work member on its support means, a connecting rod connecting thecrankshaft to said lever at a point separated from said mass and saidfirst point, and means for tuning the tunable resilient means.

3. A vibratory drive system that comprises, in combination, a base, awork member, resilient support means that support the work member fromthe base for vibration at a resonant frequency, a lever having a firstpoint pivotally connected to the work member, a mass on the lever remotefrom said first point, tunable resilient means connecting that portionof the lever carrying said mass to the work member, a crankshaftjournaled on the base that is driven at a speed in the order of but notequal to the resonant frequency of the work member on the support means,a connecting rod connecting the crankshaft to a point of the leverintermediate the mass and the first point,

means for tuning the tunable resilient means.

4. A vibratory drive system that comprises, in combination, a base, aWork member, resilient support means that support the Work member fromthe base for vibration at a resonant frequency, a lever having a pair ofspaced apart pivot points and a mass remote from said points, one ofsaid points being connected to the work member, tunable resilient meansconnecting the mass to the work member, a crankshaft journaled on thebase that is driven at a speed near but not equal to said resonantfrequency, a connecting rod connected from said crankshaft to the otherof said pair of points, and means for tuning said tunable resilientmeans.

5. A vibratory drive system that comprises, in combination, a base, avibratory work member, means for supporting the work member from thebase for movement along a work path, a lever having a pair of spacedapart pivot points and a mass spaced from said points, one of saidpoints being connected to the work member, means fixed relative to thebase for applying vibratory force to the other of said points, tunableresilient means connecting the mass to the work member, and means fortuning the tunable means.

6. A vibratory drive system that comprises, in combination, a base, avibratory work member, means supporting the work member from the basefor movement along a Work path, a lever having a mass carried on oneend, tunable resilient means connecting the mass to the work member,pivot means connecting a point of the lever remote from the mass to thework member, a crankshaft journaled on the base that is driven at asubstantially constant speed, a connecting rod connected between thecrankshaft and a 'point of the lever intermediate the mass and the firstpoint, and means for tuning the tunable resilient means.

References Cited by the Examiner UNITED STATES PATENTS 1,722,767 7/29Schieferstein 74-26 2,947,181 8/60 Carrier et a1 74-26 2, 947,410 8/60Carrier 74-26 2,984,339 5/61 Musschoot 74-87 X 3,019,889 2/62 Carrier.3,024,663 3/62 Carrier 74-26 FOREIGN PATENTS 515,267 1/31 Germany. 495,498 1 1/ 3 8 Great Britain.

BROUGHTON G. DURHAM, Primary Examiner.

1. A VIBRATORY DRIVE SYSTEM THAT COMPRISES, IN COMBINATION, A BASE OFWORK MEMBER, RESILIENT MEANS SUPPORTING THE WORK MEMBER FROM THE BASE, ADIFFERENTIAL MECHANISM HAVING A FIRST POINT CONNECTED TO THE WORKMEMBER, A MASS CONNECTED TO ANOTHER POINT OF THE MECHANISM, TUNABLERESILIENT MEANS CONNECTING SAID MASS TO THE WORK MEMBER, A CRANK SHAFTTHAT IS JOURNALED ON THE BASE, SAID CRANKSHAFT BEING OPERATED AT ASUBSTANTIALLY CONSTANT SPEED AND BEING CONNECTED TO THE DIFFERENTIALMECHANISM, AND MEANS FOR TUNING SAID TUNABLE RESILIENT MEANS.